1. Field of Invention
The present invention is related to a semiconductor device, and in particular to a reduced surface field (RESURF) structure and a lateral diffused metal oxide semiconductor (LDMOS) device including the structure.
2. Description of Related Art
In recent years, LDMOS devices have been widely used in all types of power integrated circuits or smart power integrated circuits. Operation of an LDMOS device requires a high breakdown voltage and a low on-state resistance (Ron), so that performance of the device is enhanced. In order to obtain a high breakdown voltage and a low on-state resistance, a type of so-called RESURF LDMOS device is accordingly developed. The main operation principle is that a P-type doped region is implanted in an N-type drifting region below a field oxide layer. When a reverse bias voltage is applied to the N-type region and P-type region in the device area, charges in the N-type and P-type regions need to be balanced to achieve a high breakdown voltage. Since the P-type doped region is added, the concentration in the N-type doped drifting region must be increased, and thus the on-state resistance is reduced.
Generally, the doped region which is used for reducing a surface field in the LDMOS device is formed by a single implantation method to form a layer under the field oxide layer. The doped region is limited by the implantation energy and can only be formed at the surface, so that only 1-dimensional charge balancing can be achieved, and device performance is only enhanced to a limited extent.